An update of the risk assessment for methylchloroisothiazolinone methylisothiazolinone (MCI/MI) with focus on rinse-off products

Methylchloroisothiazolinone/methylisothiazolinone (MCI/MI) has been widely used during the last 20 years for the preservation of aqueous systems in cosmetics, toiletries and in various industrial applications. MCI/MI has a broad spectrum of activity against fungi and bacteria at very low concentrations. The allergic contact potential of MCI/MI has been known for many years. This paper provides a review of pre-clinical and clinical experimental studies as well as experience from dermatology clinics worldwide. This forms the basis for an update of the risk assessment for the use of MCI/MI in rinse-off products. The scientific data indicate that the actual sensitization rate observed with a contact allergen is extremely dependent on dose and type of exposure. This review of the data leads to the conclusion that, under normal use conditions, within the current permitted/recommended use concentrations for MCI/MI of up to 15ppm, the risk of primary sensitization from the use of rinse-off products is negligible, and elicitation of allergic contact dermatitis in MCI/MI-sensitized individuals rare, after exposure to MCI/MI-preserved rinse-off products.